In ischemic heart diseases, coronary occlusion or stenosis impedes the blood flow to the cardiac muscle. Shortage or stop of the blood supply to the cardiac muscle leads to heart disorders. Patients complain of pain or oppressive feeling in the precordia, left arm, or back. A patient suffering from a disease of this type may be treated with one of pharmacotherapy, PCI (catheterization), and bypass operation.
In the pharmacotherapy, the patient is administered a drug to improve the ischemia in the heart or prevent formation of blood clots.
In the PCI, a thin tubular treatment instrument is directly inserted into a blood vessel in which occlusion or stenosis has occurred, thereby forcibly extending the blood vessel. However, if the coronary artery has an advanced three-vessel disease, chronic complete occlusion, or the like, it is difficult to conduct PCI.
The bypass operation is considered for a patient who is in a severe condition and cannot have a treatment by PCI. The bypass operation is a technique also called CABG (Coronary Artery Bypass Grafting).
In the CABG, a narrowed or occluded blood vessel is connected to another blood vessel (graft vessel) so as to flow the blood to the ischemic part via the graft vessel, as shown in FIGS. 14 and 15.
In FIG. 14, reference numeral 2 shows the Right coronary artery. Reference numeral 7 shows the Left coronary artery. Reference numeral 31 shows the Left main trunk. Reference numeral 9 shows the Circumflex artery. Reference numeral 10 shows the Anterior descending branch.
In FIG. 15, reference numeral 32 shows the Internal thoracic artery graft. Reference numeral 33 shows the Radial artery graft. Reference numeral 34 shows the Great saphenous vein graft.
The graft vessel is taken from the internal thoracic artery or great saphenous vein. When the internal thoracic artery is used, the incidence of restenosis is low, and the prognosis is good, as is known.
FFR (Fractional Flow Reserve) is an index used to select which one of PCI and pharmacotherapy is to be applied. The degree of progress of stenosis is inspected by, for example, directly inserting a pressure wire into a blood vessel. The pressure wire 35 is inserted into the blood vessel, as shown in FIG. 16, to measure pressures Pin and Pout before and after the narrow parts 36.
The FFR is defined by Pout/Pin. If the FFR is lower than 0.8, PCI is selected as the treatment. If higher, pharmacotherapy is selected. However, since inserting the pressure wire into the blood vessel is invasive, there is a demand for a noninvasive pressure measurement method and FFR estimation method.
There has been devised a method of calculating an FFR estimation value by a simulation. A technique of this type inputs a blood vessel shape acquired from modality and physical parameters such as the viscosity value of the blood or the like to a simulator. The FFR is estimated (calculated) by fluid analysis using Navier-Stokes equations used in CFD (Computational Fluid Dynamics).
An existing simulation uses a 3D image. However, since the 3D simulation needs a long calculation time, the simulation using a 3D image is 2D-approximated, thereby greatly shortening the time necessary for the simulation. This contrivance enables to quickly calculate the FFR on a simulation base. The FFR based on the approximate simulation is widely recognized as an effective index.
When CABG is selected as the treatment, it is necessary to determine the connection position of the graft vessel in the preoperative plan. The doctor confirms the state of the blood vessel by diagnostically interpreting medical images obtained by CTA (CT Angiography) or the like, and determines the connection position. However, it is difficult to interpret details of the blood vessel state. Hence, the interpreter is heavily burdened, and the possibility of oversight is undeniable. If a stenosis on the downstream side of the connection position is overlooked, the function of the cardiac muscle cannot recover, and the operation fails.